BS ISO IEC 15420-2009 pdf Information technology一 Automatic identification and data capture techniques EAN/UPC bar code symbology specification

4.3.8 Magnification factors Symbols may be reduced or enlarged from the nominal size by applying a constant magnification factor in the range 0,8 to 2,0 to all dimensions. The magnification factor of the add-on symbol shall be the same as the magnification factor of the associated main symbol. Note: In applications defined by the GS1 General specifications, symbols may be reduced or enlarged from the nominal size by applying a constant magnification factor in the range 0,8 to 2,0 to all dimensions. Under the exceptional circumstances defined in the GS1 General Specifications, the range is extended to 0,75 to 2,0. When the magnification factor is reduced below 0,8 in these applications, the minimum quiet zones and bar height shall not be reduced below the dimensions applicable to a 0,8 magnification symbol. 4.3.9 Dimensional Tolerances The historical element tolerances shown in Annex F have been superseded by the test specifications in 4.5. 4.4 Reference decode algorithm Bar code reading systems are designed to read imperfect symbols to the extent that practical algorithms permit. This section describes the reference decode algorithm used to determine decode and decodability in symbol verification in accordance with 4.5. For each symbol character, let S equal the total measured width of the character. The value S is used to determine reference threshold (RT) values. Individual edge to similar edge measurements (e) are then compared to the Reference Threshold (RT) to determine E values. Character values are determined from E values and b values according to Table 10. Value e1 is defined as the measurement from the leading edge of a bar to the leading edge of the adjacent bar. Value e2 is defined as the measurement from the trailing edge of a bar to the trailing edge of the adjacent bar. The values b1 and b2 are the measurement from the leading edge of a bar to the trailing edge of the same bar.